Mandarin hybrid tree named ‘TDE2’

ABSTRACT

A new mandarin hybrid called ‘TDE2’ is distinguished by production of fruit that combines late season maturity, large fruit size, attractive deep orange rind color and virtual absence of seeds with rich fruit flavor.

Genus and species: This application is directed to a description ofTDE2, which is a mandarin orange tree (Citrus reticulata).

BACKGROUND OF THE INVENTION

The pedigree of TDE2 is shown in FIG. 1. In 1973, pollen from Encoremandarin (unpatented) was applied to stigmas of a tetraploid (Temple×4NDancy) hybrid (unpatented) and the pollinated flowers were bagged toprevent insect pollination. Fruits were collected in winter 1974, seedsextracted from each fruit, and each seed was planted. The chromosomenumber of each seedling was determined and those identified as triploidseedlings were budded onto Troyer citrange rootstock. The resultingtrees were planted in the field in Riverside, Calif. in 1976. Thesetrees were evaluated for tree vigor, bearing, and seedlings, fruitflavor, fruit color, and other fruit quality traits from bearing until1985. Five trees were selected from the original population andrepropagated by budding onto C-32 citrange, C-35 citrange, Troyercitrange, and trifoliate orange rootstocks. One of these trees, nowcalled TDE2, was selected and further asexually propagated. Two trees ofthe selection now called TDE2 were planted in the field in Riverside in1987. When they began fruiting (approximately in 1990), these two treeswere evaluated for the same tree and fruit quality traits as theoriginal trees. In 1987, the selection now called TDE2 was chosen foradditional testing because it combined medium or large fruit size, lowseed number, rich fruit flavor, deep orange rind and flesh color, andacceptable peelability. Budwood of this selection was tested for virusesand other pathogens by the Citrus Clonal Protection Program andvirus-free bud source trees were planted at Lindcove Research andExtension Center, Exeter, Calif. in 1991.

Using this virus-free budwood source, additional trees were propagatedand planted at several California locations between 1993 and 1996. Theseincluded two locations in the Coachella Valley (Thermal, 73 trees, andthe Coachella Valley Agricultural Research Station-CVARS, 4 trees), Ojai(12 trees) and Santa Paula (6 trees) in Ventura Co., and Valley Center(11 trees) in San Diego Co. These trial plantings provide most of theavailable data on TDE2. Several different rootstocks have been used inthese evaluations, mostly Carrizo citrange, C35 citrange, and Schaubrough lemon. The trees in Valley Center are topworked Valencia orange onTroyer citrange rootstock. In general, no major effects of theserootstocks on fruit quality of TDE2 were observed, and noincompatibilities have been evident, but longevity of trees on variousrootstocks is not known.

ASEXUAL REPRODUCTION

The plant known as TDE2 was first asexually propagated in 1975 when budswere collected from hybrid seedling 73-47-2 and grafted onto Troyercitrange rootstock in a greenhouse at the University of California,Riverside, Calif., U.S.A. This tree was grown in a greenhouse and in1976 it was planted in Field 6D, Row 12, Tree 6 at the Citrus ResearchCenter, University of California, Riverside, Calif., U.S.A. Additionalasexual propagation took place in 1986 when buds were collected fromfield tree 6D-12,6 and grafted onto ‘C32’ citrange and trifoliate orangerootstocks. These trees were planted in Field 6C, Row 29, Tree positions11 and 12 respectively in 1987.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a novel mandarin hybrid having thecharacteristics described and illustrated herein. The hybrid, TDE2,produces fruit that combines late season maturity, large fruit size,attractive deep orange rind color and virtual absence of seeds with richfruit flavor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the pedigree of TDE2. All cultivars are C. reticulataexcept orange, which is C. sinensis.

FIG. 2 illustrates, clockwise from top left: a nine-year-old tree ofTDE2 on Carrizo rootstock, fruit on tree; branching pattern; flowerbuds; flowers; leaves; and shoots.

FIG. 3 illustrates fruit of TDE2 sampled from nine-year-old tree onCarrizo rootstock.

FIG. 4 illustrates the solids:acid ratio of TDE2 at Santa Paula, Calif.over five years. Points plotted are means of all samples collected on agiven date. Solid lines connect means for sampling dates within the sameseason. The dashed line is a liner regression of solids:acid on samplingdate using data from all years. The regression equation and r² value areshown in each figure.

FIG. 5 illustrates the solids:acid ratio of TDE2 at Valley Center,Calif. over five years. Points plotted are means of all samplescollected on a given date. Solid lines connect means for sampling dateswithin the same season. The dashed line is a liner regression ofsolids:acid on sampling date using data from all years. The regressionequation and r² value are shown in each figure.

FIG. 6 illustrates the solids:acid of TDE2 at Ojai, Calif. over fiveyears. Points plotted are means of all samples collected on a givendate. Solid lines connect means for sampling dates within the sameseason. The dashed line is a liner regression of solids:acid on samplingdate using data from all years. The regression equation and r² value areshown in each figure.

FIG. 7 illustrates the solids:acid ratio of TDE2 at Thermal, Calif. overfive years. Points plotted are means of all samples collected on a givendate. Solid lines connect means for sampling dates within the sameseason. The dashed line is a liner regression of solids:acid on samplingdate using data from all years. The regression equation and r² value areshown in each figure.

FIG. 8 illustrates the solids:acid ratio of TDE2 at Coachella Valley,Calif., CVARS, over five years. Points plotted are means of all samplescollected on a given date. Solid lines connect means for sampling dateswithin the same season. The dashed line is a liner regression ofsolids:acid on sampling date using data from all years. The regressionequation and r² value are shown in each figure.

DETAILED DESCRIPTION OF THE INVENTION

All major color code designation are by reference to The R.H.S. ColourChart (2001) provided by The Royal Horticultural Society of GreatBritain.

Eight to ten year-old trees grown in the ground were examined to preparethe description in this and the following paragraph. Tree shape isapproximately sphereoid (FIG. 2), rather similar to that of orangetrees. The trees have not been noted as particularly susceptible to anydiseases and, based on a freeze in 1999, appeared only slightly morecold hardy than oranges of similar age. Leaves (FIG. 2) are simple,brevipetiolate (i.e., petiole shorter than leaf lamina), lanceolate,with entire or slightly sinuate margins. The petiole shape is narrow andlinear in shape. In comparison with mold old-line citrus cultivars,trees of TDE2 are very thorny, with normal branches having medium length(15 mm) thorns at about 50% of the nodes, and watersprouts having long(31 mm) thorns at about 73% of nodes. Thorniness will probably decreaseas the cultivar ages.

Flowers of TDE2 are typically hermaphroditic, with white (Green-White157D, R.H.S. Colour Chart) petals and yellow (Yellow 13B, R.H.S. ColourChart) anthers (FIG. 2). Trees flower from early April into May at mostlocations. Pollen is somewhat sparse, with 10% viability as estimated inan in vitro germination test. Pollen tube growth was also less vigorousthan that of fertile, diploid mandarins.

The height and spread of a mature (27 years old) TDE2 tree is asfollows: Tree height=6.0 m; Width=6.0 m. Trunk diameter of a 27 year oldtree was 21.7 cm when measured 38 cm above the ground. Trunk color usingthe R.H.S. Colour Chart is Brown N200B.

-   Leaf characteristics of TDE2 trees are as follows:    -   -   Leaf shape.—Lanceolate.        -   Blade length.—82.8 mm.        -   Blade width.—43.5 mm.        -   Apex description.—Acute with weak emargination.        -   Base description.—Convex.        -   Abaxial color (R.H.S. chart).—Yellow Green 146A.        -   Adaxial color (R.H.S. chart).—Yellow Green 147A.-   Petiole characteristics of TDE2 trees are as follows:    -   -   Petiole length.—11.2 mm.        -   Petiole width.—2.3 mm.        -   Petiole color (R.H.S. chart).—Yellow Green 147A.

If sufficient fruit was available, 10-fruit samples were collected fromeach location two or three times each year beginning in 1997 or 1998.Generally samples were collected from two or three trees on eachsampling date. These fruit were evaluated in Riverside for a range oftraits as summarized in Table 1.

TABLE 1 Fruit characteristics of TDE2 averaged over 5 locations and 4seasons. Samples were collected from mid-January to early May at SantaPaula, Ojai, and Valley Center, and from mid-November to early April atThermal and CVARS. “N” indicates the total number of fruit samplesanalyzed. Data shown are averaged over fruit from trees on variousrootstocks. The trees examined for TabIe 1 ranged from 3-8 years old andwere grown in the ground. Trait N Min Max Min SD Fruit height (mm) 14938.7 80.0 58.4 6.46 Fruit width (mm) 149 57.5 91.6 74.5 5.71 Fruitheight:width 149 0.52 0.94 0.78 0.064 Rind color rating^(a) 149 4.5 13.011.8 1.08 Rind texture^(b) 149 2.2 7.5 3.7 0.68 Neck rating^(c) 149 02.50 0.47 0.66 Peelability rating^(d) 149 6.00 9.50 7.91 0.736 Rindthickness (mm) 149 3.00 6.00 3.86 0.626 Seeds per fruit 149 0 0.40 0.020.065 Fruit weight (g) 149 103.5 370.0 184.5 45.12 Juice content (%) 14932.4 62.5 49.4 4.911 Soluble solids (%) 146 7.50 15.55 12.38 1.749 Acid(%) 145 0.62 2.64 1.22 0.341 Solids:acid 145 4.10 22.90 10.84 3.204^(a)Visual rating on a scate of 0-13; 0 = green, 13 = red-orange^(b)Visual rating on a scale of 1-8; 1 = very smooth, 8 = extremelycoarse ^(c)Visual rating on a scale of 0-3; 0 = no trace of neck, 3 =neck with a diameter at least 50% of fruit diameter ^(d)Subjectiverating of ease of peeling a single fruit; 1 = very difficult, 10 = afruit with completely seperated rind and segments. Fruit with ratings of7 or higher would be relatively easy to peel.

Based on this data, TDE2 fruit are oblate in shape, with little or noneck (FIG. 3). The average fruit size is large for a mandarin (classedas Mammoth by California state standards). Rind color of mature fruit isorange-red N30D (R.H.S. chart). The rind texture is variable, dependingon tree age and crop. For older trees with a moderate to heavy crop,rind texture is slightly pitted, with depressed oil glands. The rind offruit from trees with very light crops is often excessively rough orbumpy. The rind is fairly easy to peel when fruit are mature, but can bemore adherent early in the season. The fruit flesh color using theR.H.S. chart is orange 28B. Flesh thickness is about 68 mm. Albedo coloris Yellow-White 158C. Albedo thickness is about 2.0 mm. Adherence ofrind to pulp is medium or moderate. The number of segments per fruit is9-10. The fruit base (stalk end) is slightly concave (FIG. 3), and theapex is truncate with a slight depression in the stylar end and a small(4 mm), occasionally open stylar scar.

Important determinants of maturity date for citrus fruit are thesolids:acid ratio and juice content. Using data for all years, juicecontent did not show a statistically significant correlation withsampling date at any of the 5 locations. This indicates that there wasnot generally any significant drying of fruit during the samplingperiod. Solids:acids ratio was significantly correlated with samplingdate at all location except Santa Paula (FIG. 4). Using theseregressions, the estimated dates on which fruit reached an 8:1solids:acid was December 6 for Thermal, January 2 for Ojai, February 20for Valley Center, and March 5 for Santa Paula. The limited data forCVARS are consistent with those for the climatically similar Thermalsite.

Yield of TDE2 was evaluated from visual ratings of crop relative to treesize at each location from 1998-99 to 2001-2002. The rating scale rangedfrom 0 (no crop) to 5 (very heavy crop). The topworked trees in ValleyCenter showed the highest and most consistent crops, ranging between 3and 4 over the 4 years studied. Crops at Ojai were also good, being 2.5or greater in all years. At Santa Paula, crop ratings indicatedalternate bearing, with average values of 2.17, 3.67, 1.17, and 3.50from 1998-99 to 2001-2002, respectively. Trees planted at Thermal in1994 showed similar behavior, but with lower values of 1.83, 0.50, 2.40,and 1.40, while those planted in 1996 had crops of 0, 0, 2.87, and 1.5.

As discussed above, tree fruit is set in April and May. First and lastharvest dates for Riverside Calif. are estimated as February 15 and May15. Because TDE2 is a late maturing fruit, it is likely that trees willshow a fairly strong tendency to alternate bearing, and this issupported by the data for some locations.

During the 1998-99 season, fruit of TDE2 and Gold Nugget, another lateseason mandarin with few seeds, were harvested on April 12 from ValleyCenter and evaluated by a taste panel before and after storage at twodifferent temperatures. Fruit were rated on a 9 point scale, where ascore of 1 is “Dislike extremely”, 5 is “Neither dislike or like”, and 9is “Like extremely”. Results (Table 2) show that before storage TDE2 waspreferred to Gold Nugget based on visual appearance, peelability, andtaste, with good overall scores for these traits. After storage at 20.5C for 11 days, both cultivars improved in visual appeal and peelability,but only Gold Nugget improved in taste. Storage for 12 days at 3.4 or5.6 C followed by 7 days at 13.3 C did not greatly affect any of theratings, but taste of both cultivars was decreased slightly in coldstorage at 3.4 C. Waxed fruit were similar to unwaxed for nearly alltraits. Storage at 5.6 C decreased visual appeal of TDE2 slightly whilestorage at 20.5 C increased visual appeal, peelability, and tastescores. Overall, these data indicate that TDE2 fruit can be storedwithout greatly affecting visual appeal or taste.

TABLE 2 Sensory evaluation of ‘Gold Nugget’ and ‘TDE 2’ harvested April12, 1999 from Valley Center, CA. Visual Evaluation Gold Gold NuggetNugget TDE 2 TDE 2 −wax +wax −wax +wax Initial Mean 4.3 5.0 6.8 7.0 SD2.1 2.0 1.6 1.5 11 days @ 68 F. Mean 5.4 6.2 7.3 7.9 SD 1.6 1.5 1.4 0.912 days @ 37 F. + 7 days @ 55 F. Mean 5.3 5.7 6.8 7.2 SD. 2.5 2.1 1.31.5 12 days @ 41 F. + 7 days @ 55 F. Mean 5.5 5.7 7.4 7.1 SD. 2.3 2.11.4 1.4 Peelability Evaluation Gold Gold Nugget Nugget TDE 2 TDE 2 −wax+wax −wax +wax Initial Mean 4.6 4.0 7.0 6.8 SD 1.7 1.9 1.3 1.5 11 days @68 F. Mean 5.3 5.4 7.6 7.5 SD 2.1 2.2 1.1 0.8 12 days @ 37 F. + 7 days @55 F. Mean 5.2 5.6 7.1 7.2 SD. 1.7 1.9 1.6 1.5 12 days @ 41 F. + 7 days@ 55 F. Mean 6.1 5.2 7.4 7.3 SD. 1.4 1.7 1.4 1.5 Taste Evaluation GoldGold Nugget Nugget TDE 2 TDE 2 −wax +wax −wax +wax Initial Mean 5.4 5.36.5 6.8 SD 2.0 2.6 1.6 1.7 11 days @ 68 F. Mean 7.3 6.8 6.5 5.7 SD 1.71.9 1.7 1.6 12 days @ 37 F. + 7 days @ 55 F. Mean 6.1 6.0 5.8 6.3 SD.1.9 2.4 1.6 1.5 12 days @ 41 F. + 7 days @ 55 F. Mean 6.5 6.6 6.9 6.5SD. 1.6 1.6 1.4 1.7

Two siblings of TDE2, “TDE3” and “TDE4,” were compared to TDE2. TDE2 isdistinct from these cultivars in having the latest maturity date, thelargest fruit size, a more oblate shape than TDE3, and distinct flavor.The rind color of TDE2 is usually paler orange than that of TDE4. Treesor fruit of TDE2 can be distinguished from those of other mandarins,including TDE3 and TDE4, using simple sequence repeat (SSR) DNA markers.Using TDE2 DNA as template, PCR primer set TAA15(F=GAAAGGGTTACTTGACCAGGC, R=CTTCCCAGCTGCACAAGC) amplified a band of 185bp, while TDE3 and TDE4 both had two bands of 185 and 200 bp. Bandsamplified with TAA15 combined with those amplified with either CAC15(F=TAAATCTCCACTCTGCAAAAGC, R=GATAGGAAGCGTCGTAGACCC) or TAA33(F=GGTACTGATAGTACTGCGGCG, R=GCTAATCGCTACGTCTTCGC) distinguished TDE2from the following cultivars: Dancy (unpatented), Temple (unpatented),Encore (unpatented), King (unpatented), Willowleaf (unpatented), Wilking(unpatented), Gold Nugget (unpatented), Pixie (unpatented), W. Murcott(unpatented), Ellendale (unpatented), Hernandina Clementine(unpatented), Fortune (unpatented), Kara (unpatented), Kinnow(unpatented), Murcott (unpatented), Nova (unpatented), and Ponkan(unpatented).

The seed (female) parent of TDE2 is a tetraploid hybrid between a‘Temple’ tangor and a tetraploid tree of ‘Dancy’ mandarin. Thetetraploid (Temple×4N Dancy) parent (referred to below as 4D-TD) wasnever released by the University of California and only two trees ofthis variety exist. TDE2 is distinct from this variety in having lessthan 1 seed per fruit while 4N-TD averages 10 seeds per fruit. Fruit of4N-TD have an aspect of about 0.88, mature in December-January and holdon the tree for about 1 month, while those of TDE2 have an aspect ratioof about 0.78, mature in February and hold on the tree for 2-3 months.Fruit of 4N-TD have thicker rinds (5.5 mm) than those of TDE2. Trees of4N-TD are somewhat smaller (3.8 m tall) than those of TDE2 (6.0 m tall).

The pollen (male) parent of TDE2 is ‘Encore’ mandarin. TDE2 differs from‘Encore’ in that ‘Encore’ fruit average about 20 seeds per fruit whilefruit of TDE2 have less than 1 seed per fruit. ‘Encore’ fruit mature inMarch-April, about 1 month later than those of TDE2. ‘Encore’ fruitalways have a distinctive green or dark brown spot or blotch on the rindwhich is absent on TDE2 fruit. The average size of TDE2 fruit is largerthan that of Encore. Encore fruit have an aspect ratio of 0.71 and muchthinner rinds (2.0 mm) while those of TDE2 have an aspect ratio of 0.78and rinds 3.5 mm thick. Encore fruit hold extremely well on the tree(4-6 months). The height of mature (35 year old) ‘Encore’ trees is about4.1 m, shorter than that of mature (27 year old) TDE2 trees.

Vigor of TDE2 trees has varied greatly across locations. In the twodesert locations, canopy volumes of 7-year-old trees averaged 41.1 and28.8 m³, and 5 year-old trees averaged were 9.7 m³. In contrast, at thecooler Santa Paula and Ojai locations, 7-year-old trees averaged 6.3 and6.1 m³. Trees in the desert locations have averaged somewhat less croprelative to tree size, perhaps contributing to greater vegetativegrowth. Size of the topworked trees in Valley Center has not beenmeasured since they are not comparable to trees in other locations, butin general the topworked trees are quite vigorous. Rootstocks had someeffect on trees size. At Thermal, trees on Volkamer lemon had canopyvolumes about twice that of trees on Carrizo or C35 citranges. Trees onSchaub rough lemon were usually larger than those on Carrizo or C35citranges. No evidence of stock-scion incompatibilities was evident, buttrees are still relatively young.

TDE2 can be propagated on many available citrus rootstocks by budding.Because of the high level of thorniness, great care should be taken toselect budwood from upper-canopy branches having no thorns. Tree spacingin field plantings will depend on vigor of the rootstock. Trees can begrown with pollinizer cultivars such as Minneola, Valencia orange,unrelated mandarins (not Temple, Dancy, Encore or other TDE hybrids)that produce viable pollen. Maturity dates will vary with location,probably depending on the number of heat units and soil conditions.

As in some other mandarins, sprays with gibberellic acid may increasefruit set when pollinizers and/or pollinators are inadequate.

Trees are winter hardy in USDA zones 9b to 11.

1. A new and distinct variety of mandarin hybrid tree having thecharacteristics described and illustrated herein.